Asthma affects more than 6% of U.S. children, making it the most common chronic disease in kids nationwide. It鈥檚 difficult to isolate any single cause, but one of the most common contributors is air pollution: Studies have shown that breathing air with high levels of fine particulate matter, nitrogen dioxide and other environmental pollutants can increase children鈥檚 risk of developing asthma. But it鈥檚 been unclear whether long-term, early childhood exposure to ozone, the pollutant that most frequently exceeds U.S. air quality standards, contributes to the disease.听听
, a doctoral student at the 天美影院, set out to find a possible link. In a study , Dearborn and collaborators identified a puzzling trend: Children exposed to higher levels of ozone in their first two years of life were significantly more likely to be diagnosed with asthma or wheezing at ages 4-6 鈥� but researchers didn鈥檛 observe the increased risk of asthma at ages 8-9.听听
While the researchers couldn鈥檛 pin down the exact reason, possible explanations include the changing nature of asthma as kids age, which could lead to a drop-off in formal diagnoses, and the influence of other risk factors and pollutants on asthma as children鈥檚 lungs grow.听
鈥淚t鈥檚 a puzzling finding,鈥� said Dearborn, who led the research in the 天美影院Department of Environmental & Occupational Health Sciences. 鈥淚t鈥檚 something we spent a long time trying to consider, and I don鈥檛 know if we ever came up with a satisfying answer. But these findings are important. Even if we only see the effects early in life,听there are still all kinds of associated health care costs and stresses for families. There are all sorts of larger contextual factors about having this chronic disease at any point in life.鈥�听
This study relied on data from the (ECHO) program, a federal research project focused on how a wide range of environmental factors affect children鈥檚 health. Researchers drew 1,118 participants from six cities, including Seattle and Yakima, who had low-risk pregnancies and completed validated surveys that asked if their children had been diagnosed with asthma or had experienced wheezing.听听
Researchers estimated exposure in the first two years of a child鈥檚 life using a model developed by co-author , a 天美影院professor of environmental and occupational health sciences, of epidemiology and of medicine. They found that a relatively small increase in ozone exposure 鈥� 2 parts per billion 鈥� in a child鈥檚 first two years of life was associated with a 31% increase in asthma and 30% increase in wheeze at age 4-6 years. Asthma and wheeze risk at ages 8-9 was not found to be associated with their early life ozone concentration.听
Researchers also analyzed how exposure to mixtures of three common air pollutants 鈥� ozone, nitrogen dioxide and fine particulate matter (PM2.5) 鈥� affected asthma outcomes. In this analysis, ozone stood out.听
鈥淲e interpret trends, and what we can conclude from this analysis is that when ozone within the air pollution mixture was higher than about 25 parts per billion, we saw a higher probability of asthma regardless of the concentration of nitrogen dioxide,鈥� Dearborn said. 鈥淲e found a relationship between ozone and asthma only when fine particulate matter was at or above median concentrations, giving novel evidence that the relationship between ozone and childhood asthma may depend on the concentration of other pollutants, like fine particulate matter.鈥�听
The study鈥檚 findings highlight the need for more research into the effects of long-term ozone exposure in early life, Dearborn said. Further study could determine why the increased asthma risk related to ozone is not evident at ages 8-9, and whether it increases again later in childhood.听听
In the meantime, Dearborn said, researchers and public health officials should pay more attention to the effects of long-term exposure to ozone.听
鈥淚n the United States, ozone regulations only consider a very short time period,鈥� Dearborn said. 鈥淲e don鈥檛 regulate ozone over the long term, and that鈥檚 where this analysis fits in. Maybe we should be considering both a short- and a long-term threshold for the regulation of ozone.鈥澨�听
Other authors are , a 天美影院professor of environmental and occupational health sciences and of pediatrics in the 天美影院School of Medicine; postdoctoral researchers and , research scientist , and clinical associate professor , all of the 天美影院Department of Environmental & Occupational Health Sciences; , a 天美影院professor of biostatistics; , a graduate student in the 天美影院Department of Epidemiology; of Seattle Children鈥檚 Research Institute and an assistant professor of pediatrics in the 天美影院School of Medicine; Margaret Adgent and Paul Moore of Vanderbilt University Medical Center; Yu Ni of San Diego State University; Marnie Hazlehurst and Drew Day of Seattle Children鈥檚 Research Institute; Ruby Nguyen of the University of Minnesota; Kaja LeWinn of the University of California, San Francisco; and Kecia Carroll of the Icahn School of Medicine at Mount Sinai in New York City.听听
This research was funded by the National Institutes of Health鈥檚 ECHO-PATHWAYS program; the National Center for Advancing Translational Health Sciences; the National Heart, Lung, and Blood Institute; the National Institute of Environmental Health Sciences; the 天美影院Pediatric and Reproductive Environmental Health Scholars K-12 program; the U.S. Environmental Protection Agency; the 天美影院EDGE Center; the National Institute on Aging; and the Urban Child Institute.听